The role of sulfate-reducing bacteria in the anaerobic corrosion of mild steel and brass was studied. Culture-media containing sulfide of biogenic and of chemical origin was used to see the effect of metal-sulfide layers developed in different ways. Biocides with different efficiency were used to inhibit metabolic activity of bacteria. Polarization resistances and open circuit potentials were recorded followed by potentiostatic polarization measurements on the metal samples to get information on corrosion rates and the mechanism of corrosion processes. An atomic force microscope was used to image the topography of sulfide layers.